Acharya Prashant explains that doubting oneself does not mean doubting the soul, as the soul is beyond both doubt and belief. He uses the metaphor of a ghost to describe how the past and social conditioning take control of a person's actions, thoughts, and desires. He suggests that since we are almost entirely governed by these external influences, we must maintain a small percentage of awareness to observe and doubt our own activities. By constantly asking "Who spoke?" or "Who acted?", one begins to realize that their actions are not truly their own but are driven by the 'ghost' of the past.